### As per Newton's second law of Motion

Force = Rate of Change in Momentum

Force = Change in Momentum/Time

F = m x (v - u)/t

F = m x a

HENCE

As per Newton's Second Law of Motion

Force = Mass x Acceleration

Force/Mass = Acceleration

Acceleration = Force/Mass

### hence it can be said that

Acceleration of a body is directly proportional to Force Applied

More the force Applied,more will be the acceleration

### Also it can be said that

Acceleration of a body is inversely proportional to Massof the Object

More the mass of an object,lower will be the acceleration

Hence,it is more difficult to move heavy objects but it is easier to move lighter objects

### Questions

Example 9.2 - Which would require a greater force –– accelerating a 2 kg mass at 5 m s –2 or a 4 kg mass at 2 m s −2 ?

Example 9.4 - A force of 5 N gives a mass m1, an acceleration of 10 m s –2 and a mass m 2 , an acceleration of 20 m s −2 . What acceleration would it give if both the masses were tied together?

Example 9.5 - The velocity-time graph of a ball of mass 20 g moving along a straight line on a long table is given in Fig. 9.9.How much force does the table exert on the ball to bring it to rest?

NCERT Question 5 - A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 tonnes (Hint: 1 tonne = 1000 kg.)

NCERT Question 6 - A stone of 1 kg is thrown with a velocity of 20 m s–1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?

NCERT Question 7 - A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) the net accelerating force and
(b) the acceleration of the train.

NCERT Question 8 - An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 m s –2 ?

NCERT Question 14 - A bullet of mass 10 g travelling horizontally with a velocity of 150 m s–1 strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also calculate the magnitude of the force exerted by the wooden block on the bullet.

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1. Class 9
2. Chapter 9 Class 9 - Force and Laws Of Motion
3. Concepts

Concepts

Class 9
Chapter 9 Class 9 - Force and Laws Of Motion 